1. Field of the Invention
The present invention relates to integrated circuits and, in particular, to an integrated, high accuracy voltage regulator.
2. Discussion of the Prior Art
Microminiaturization of MOS field effect transistors (MOSFETs) is a traditional approach in the development of high density dynamic random access memories (DRAMs). However, MOSFETs of submicron geometries may suffer from source/drain punch-through as well as from substrate current. One of the solutions to this problem is reduction of the power supply voltage V.sub.CC below 5 V. This reduction in supply voltage conflicts, however, with the desire to be compatible with conventional transistor-transistor-logic (TTL) and other single 5 V power supply designs.
To resolve this conflict, an on-chip voltage regulator has been proposed by Mano et al., "Submicron VLSI Memory Circuits", 1983 IEEE International Solid State Circuit Conference, p. 234. The Mano et al. voltage converter utilizes an external 5 V power supply to feed I/O circuitry containing a relatively small number of transistors, while the main portion of the circuit is fed by a lower voltage from the converter. As shown in FIG. 1, control of the output voltage in the Mano et al. voltage converter circuit is based upon four MOSFETs M1, M2, M3 and M4 which are connected sequentially in diode configuration.
The disadvantage of the Mano et al. voltage converter design is that the source/drain punch-through voltage is tied to the threshold voltages of the four transistors M1-M4. If, for example, the threshold of each transistor varies .+-.0.2 V, then the output voltage of the converter has an uncertainty factor of .+-.0.8 V.